Triple stepper Z Axis

Hi i am buildn a ultimaker clone, but bigger...
Because of the bigger size i wanted to use 3 steppers on the z axis to avoid problems..
I thought if i use the 3 steppers it should be possible to auto calibrate the z axis using a proximity sensor..
I saw there is a options called auto leveling..
The controller i want to use is a ramps 1.4 whit triple stepper expander..
Someone did this or can give me some infos about how to implement it on the controller?
What proximity sensor to use? capacitive, inductive or ultrasonic - analog or digital?
Thanks

The biggest problem with multiple steppers on the Z axis is keeping them in sync because when you first power up the machine, they will all jump to the nearest whole step. Some will jump forwards and some will jump backwards so after a number of power cycles, the problem will be exacerbated. For info, my bed weighs around 7Kg and is lifted using 3 screws but with a continuous belt and a single Nema 17 motor with 1:1 gearing.

Quoteo5i
Hi i am buildn a ultimaker clone, but bigger...
Because of the bigger size i wanted to use 3 steppers on the z axis to avoid problems..
I thought if i use the 3 steppers it should be possible to auto calibrate the z axis using a proximity sensor..
I saw there is a options called auto leveling..

I have exactly this sort of auto levelling on my work list for RepRapFirmware. But it's 32-bit firmware so it doesn't run on RAMPS. If you are going to build a large, expensive printer, I suggest you use good electronics in it anyway instead of budget electronics such as RAMPS.

That depends on your print bed surface. Take a look at the differential IR sensor that I sell, which works well with most bed surfaces, although some like PEI need to be prepared in a certain way. See [miscsolutions.wordpress.com].

Quotedeckingman
The biggest problem with multiple steppers on the Z axis is keeping them in sync because when you first power up the machine, they will all jump to the nearest whole step. Some will jump forwards and some will jump backwards so after a number of power cycles, the problem will be exacerbated. For info, my bed weighs around 7Kg and is lifted using 3 screws but with a continuous belt and a single Nema 17 motor with 1:1 gearing.

Actually they jump to the nearest multiple of 4 full steps that matches the phase currents. I'll be adding code to avoid this issue in RepRapFirmware for the Duet WiFi, by detecting power down and moving each motor to one of the correct positions ready for power up. I can do this because the Duet WiFi has two power monitor circuits on board. However, with the planned auto levelling, it won't matter if the motors jump a bit when you cycle power, if you run auto level every time you power on.

Couldn't the same calibration result be achieved by pushing the motors in question to a known axis limit and then, once that's triggered, push them a bit longer until they error out due to not being able to push farther?

I can't say if this was done on IBM PC floppy drives, but the Apple ][ series determined which was track 0 or 35 by deliberately going enough steps to guarantee it'd get to the limit: in other words, it'd go until it crashed, then it kept beating the read/write head against the limit. While it was crude and made a bit of noise, it worked.

i have a utimaker clone whit triple z axis and z probe.. what i want is adjust the bed to be flat automaticly by measuring the distance on 3 points of the bed (where the steppers are) its like a triangle... i saw that it is possible but what firmware is the best to use in this case?

Ok, you mean true automatic bed levelling. I am not aware of any firmware that supports it properly yet, although RepRapFirmware lets you get close, see [www.duet3d.com]. It's on my list to support it natively in RRF and some of the preparatory code has already been implemented in the latest beta firmware.